DNA profiles are routinely used in criminal, paternity, and human identification procedures. The US military requires samples from every soldier, and every state in America requires DNA samples from convicted offenders of qualifying crimes. In addition to these targeted groups, many people are asked to give samples as victims or suspects of crimes.
Reference samples are those given by (or obtained from) known individuals who are part of a forensic, medical, legal or other identification investigation. These samples may be obtained from living or deceased individuals, or from items presumed to be derived from those individuals. A typical example is a blood or buccal sample obtained from a suspect in a criminal investigation.
Once reference samples are obtained, the integrity of the subsequent investigation and analysis depends on the integrity of the reference samples. An investigation can be completely compromised by the cross contamination of reference sample and evidentiary material. There is presently no standard marker added to blood, buccal or other biological reference samples which prevents their accidental or malicious deposition at crime scenes, or in or on evidence samples. In addition, it is not uncommon for the same individuals to handle reference and evidentiary samples. Should cross-contamination occur there is no reliable mechanism of demonstrating that it has happened.
Biological samples are now taken as a standard part of numerous forensic, medical, legal and identification procedures. Several states have enacted legislation defining the length of time that state agencies and forensic laboratories can hold reference samples, but others can hold these samples indefinitely. This has led to a concern on the part of those who provide the samples that errors or malicious intent could lead to their samples being mishandled, thus implicating them in criminal activity. While the DNA in a biological sample serves as an individuating identification of the donor, it says nothing of the manner in which it was obtained. The vast majority of DNA samples are taken as reference samples (known identity), and these must remain separate from evidentiary samples (unknown samples). While several patents address the labeling of samples with chemical markers, none of them satisfy the issues inherent in forensic DNA analysis.
U.S. Patent Application No. 20040072199 discloses a method for marking samples containing DNA by means of oligonucleotides. This invention does not address forensic applications, and the oligomers disclosed are artificial microsatellites and single nucleotide polymorphisms, designed without reference to avoiding sequences that might be encountered in typical forensic samples.
WO 96/17954 discloses a method for chemical identification of an object, wherein according to the invention at least two chemical markers are used. One marker shows that the container itself has been marked, while the other marker is in principle the real identification. However, such markings are not based on DNA sequences that would be readily detectable using the methodologies common in forensic, paternity and human identification laboratories.
U.S. Pat. No. 5,776,737 discloses a method for the identification of samples, wherein oligonucleotides are added to the sample obtained, which will be sequenced together with the sample after a subsequent amplification step. The oligonucleotides consist of a primer binding site and an identification region consisting of an alternating sequence of nucleotides (MN)x and (MNN)x, respectively, wherein N is the nucleotide of the primer binding site. The sample can be identified by sequencing the identification region. However, this method requires sequencing, and does not address the question of oligomer design in terms of avoiding sequences commonly encountered in forensic samples.
International Patent No. 20030177095 describes a system of authentication and/or tracking for identifying, tracking, authenticating and/or otherwise checking the legitimacy of one or more items which include a coded identity tag or mark, the system comprising identification means for reading said coded identity tag or mark and identifying said one or more items, storage means for storing information relating to the location, whether actual or intended, origin and/or ownership of said one or more items, and means for displaying or otherwise providing or verifying said information relating to an item when its identity tag or mark has been read. However, this system does not cover the specific application of identifying biological reference samples in order to distinguish them from evidentiary samples. It also does not embody a tag that will be identified using the standard techniques in use by forensic, medical, legal and identification laboratories namely Polymerase Chain Reaction and mitochondrial DNA sequencing. Rather it applies to a system which uses tags “preferably in the form of a coded fibre or filament” (claim 3); which can be read by a “bar code reader or scanner” (claim 4). While the claim mentions DNA in its summary (2) as a possible “tag” it does not describe any specific applications or methods using DNA as a tag.
Several patents describe forensic primer sets which are used to amplify human short tandem repeat (STR) regions of the genome. For example, U.S. Pat. No. 6,251,592, for example, discloses (Short Tandem Repeat) STR markers for DNA fingerprinting. This patent is a refinement on the standard technology of DNA fingerprinting for human identification using STR markers.
The prior art has thus far failed to provide a system whereby nucleic acid samples such as forensic reference samples can be marked with amplifiable DNA tags to distinguish the samples from other unmarked samples, thereby establishing their authenticity in a manner compatible with common identification methods such as forensic profiling.